Dual spectrum infrared fire detection system with high energy ammunition round discrimination

ABSTRACT

Disclosed is a multichannel fire or explosion detection system wherein an output fire suppression or control signal is generated in response to fires or explosions which radiate power above a predetermined threshold level. The system includes means which discriminate against explosive fires in a fuel tank or other highly combustible material on the one hand and high energy exploding rounds of ammunition per se which do not subsequently cause a large scale fire. Thus, the present detection system will not generate an output fire suppression or control signal in the event a high energy ammunition round explodes in the vicinity of a fuel tank without igniting and exploding it. Additionally, fail safe detection logic means are provided in the present system and generate a time delayed fire suppression enable signal to thereby enable an output signal gate in the event of a delayed or secondary fire or explosion above a predetermined magnitude.



1. A system for making energy dissipation comparisons while detecting fires and explosions above predetermined power thresholds within predetermined time periods including: a. low threshold radiation channel means responsive to minimum power fires or explosions for generating output enable signals, b. high threshold raDiation channel means responsive to fires or explosions which exceed a predetermined energy threshold for generating inhibit signals of a predetermined time duration or durations, and c. output logic gate means coupled to both said low and high threshold radiation channel means for receiving both said enable and inhibit signals, said output logic means being operative to generate an output fire control or suppression signal after the removal of said inhibit signals therefrom, whereby relatively short lived fires or explosions within the time duration of said inhibit signals are prevented from triggering an output fire detection or control signal.
 2. The system defined in claim 1 wherein said high threshold radiation channel means includes: a. a threshold gate of a selected switching threshold connected in the signal path of said high threshold channel means and operative to generate logic signals of a time duration dependent upon the energy received from a fire or explosion, b. first pulse delay generating means connected between said threshold gate and one input of said output logic gate means for generating a first inhibit signal of a first predetermined time duration, and c. second pulse delay generating means coupled between said threshold gate and another input of said output logic gate means for generating a second inhibit signal of a second predetermined time duration, whereby said output logic gate means is enabled to generate a fire control or suppression signal after the termination of said inhibit signals and in the continued presence of enable signals from said low threshold radiation channel means.
 3. The system defined in claim 2 which further includes: a. a second threshold gate having a second threshold switching level and connected to receive the radiation responsive detection signals from the main signal path of said high threshold channel means to thereby generate enable logic pulses of another, different predetermined time duration, and b. a second output logic gate means connected to receive both logic signals from said second threshold gate and from said second pulse delay generating means for thereby generating output fire control or suppression signals when said second output logic gate means is enabled, thereby imparting an additional level of energy discrimination to said high threshold radiation channel means.
 4. The system defined in claim 3 which further includes an output OR gate connected to receive the output signals from both said first and second output logic gate means for generating the system''s output fire control or suppression signals upon receiving enable signals from either of said first and second output logic gate means.
 5. The system defined in claim 1 wherein said low threshold radiation channel means includes: a. long wavelength channel means responsive to radiant energy in a predetermined spectral band of electromagnetic radiation and received from a fire or explosion for generating one output logic signal, b. short wavelength channel means responsive to radiant energy in another predetermined spectral band and received from said fire or explosion for generating another logic signal, and c. means coupling said one and another output logic signals to said output logic gate means for properly enabling same during the presence of a fire or explosion above a predetermined minimum threshold level.
 6. The system defined in claim 5 wherein said coupling means includes first and second signal delay stages connected in the signal paths of said long and short wavelength channel means, respectively, and further connected to first and second inputs of said first output gate means for providing delayed enable signals thereto, whereby said first output gate means is not immediately enabled after the initiation of said fire or explosion, thereby allowing said high threshold radiation channel means to properly respond to predetermined energy levels of a radiation received from said fire or explosion and thereby temporarily inhibit said first output gate means for predetermined time durations.
 7. The system defined in claim 6 wherein: a. said long wavelength channel means is responsive to radiant energy in a predetermined spectral band above about 6 microns of electromagnetic radiation, and b. said short wavelength channel means is responsive to radiant energy in a predetermined spectral band less than about 2 microns of electromagnetic radiation.
 8. The system defined in claim 7 wherein said long wavelength channel means is responsive to radiation in the 7 - 30 micron range and said short wavelength channel means is responsive to radiation in the 0.7 - 1.2 micron range, and said high threshold channel radiation means is responsive to short wavelength radiation in the 0.7 - 1.2 micron range.
 9. The system defined in claim 8 wherein: a. both said high threshold radiation channel means and said short wavelength radiation channel means includes a photodetector connected at each input thereof, and b. said long wavelength channel means includes a thermopile detector connected at its input and responsive to a radiation in a spectral band above about 6 microns of electromagnetic radiation.
 10. The system defined in claim 9 wherein said high threshold radiation channel means includes: a. a threshold gate of a selected switching threshold connected in the signal path of said high threshold channel means and operative to generate logic signals of a time duration dependent upon the energy received from a fire or explosion, b. first pulse delay generating means connected between said threshold gate and one input of said output logic gate means for generating a first inhibit signal of a first predetermined time duration, and c. second pulse delay generating means coupled between said threshold gate and another input of said output logic gate means for generating a second inhibit signal of a second predetermined time duration, whereby said output logic gate means is enabled to generate a fire control or suppression signal after the termination of said inhibit signals and in the continued presence of enable signals from said low threshold radiation channel means.
 11. The system defined in claim 10 which further includes: a. A second threshold gate having a second threshold switching level and connected to receive the radiation responsive detection signals from the main signal path of said high threshold channel means to thereby generate enable logic pulses of another, different predetermined time duration, and b. a second output logic gate means connected to receive both logic signals from said second threshold gate and from said second pulse delay generating means for thereby generating output fire control or suppression signals when said second output logic gate means is enabled, thereby imparting an additional level of energy discrimination to said high threshold radiation channel means.
 12. The system defined in claim 11 which further includes an output OR gate connected to receive the output signals from both said first and second output logic gate means for generating the system''s output fire control or suppression signals upon receiving enable signals from either of said first and second output logic gate means.
 13. A fire or explosion detection system for making predetermined energy dissipation comparisons including: a. threshold radiation channel means responsive to fires or explosions which generate a predetermined amount of energy within a predetermined period of time to in turn generate inhibit signals, and b. output gate means coupled to said radiation channel means and responsive to said inhibit signals to prevent an output fire suppression from being generated during the presence of said inhibit signals, whereby said channel is operative to generate said fire suppression signals after the termination of said inhibiT signals or in the event that no inhibit signals are generated.
 14. The system defined in claim 13 wherein said threshold radiation channel means includes logic means for generating an inhibit signal whose time duration is proportional to the time that the radiated power from said fire or explosion is above a predetermined threshold level, whereby the variable duration of said inhibit signals may be logically compared with other fixed signal delays to prevent predetermined energy levels reached in predetermined minimum times from generating an output fire control or suppression signal. 